1. Field of the Invention
The present invention relates to a servo control device for an image forming apparatus, and a recording medium.
2. Description of the Related Art
One type of an image forming apparatus such as a printer, a facsimile, a copier, a plotter, and a multi-function peripheral is an inkjet recording apparatus which discharges droplets of ink and records dots.
One type of an image forming apparatus such as a printer, a facsimile, a copier, a plotter, and a multi-function peripheral is an inkjet recording apparatus which uses a recording head discharging ink droplets. This inkjet recording apparatus discharges the ink droplets from the recording head to carried papers to thereby form images. Hereinafter, forming the images includes recording, printing characters, printing photos, printing images and so on. The image forming apparatus includes a serial-type image forming apparatus by which images are formed while the recording head moves in a main scanning direction and discharges ink droplets, and a line-type image forming apparatus by which images are formed while the recording head does not move and discharges ink droplets.
Hereinafter, “imaging apparatus of a liquid discharging type” is configured to discharge the droplet so as to hit a medium such as papers, textile threads, textiles, cloths, leathers, metals, plastics, glasses, lumber, and ceramics. Further, “imaging” means not only making of image such as a character, a letter and a figure but also causing droplets to hit the medium or giving an image such as a pattern to the medium. The “ink” is not limited to so-called inks and is an all-inclusive term of all kinds of liquids which can form images such as recording liquids, fixing agents, resins and so on. The material of “Paper” is not limited and may include OHP sheets and the above described clothes. The “Paper” is an all-inclusive term of recording media, recording papers, recording sheets and so on and represents any matter to which the ink droplets can be adhered. The “image” is not limited to a two-dimensional image, and may be an image given to a stereoscopic object or a three-dimensionally fabricated image.
Although an image forming apparatus having a liquid discharging head is exemplified, the image forming apparatus may not have the liquid discharging head and be another type.
For example, a carriage of a serial-type image forming apparatus has a liquid discharge head being an image forming unit. The liquid discharge head is moved in a main scanning direction and a recording medium is intermittently moved in a sub scanning direction orthogonal to the main scanning direction while liquid droplets are discharged from the liquid discharge head. Thus, an image is formed.
This serial-type image forming apparatus includes a linear encoder for detecting a position of the liquid discharge head. The linear encoder includes an encoder scale arranged along a main scanning direction of a carriage in which the liquid discharge head is installed and an encoder sensor for reading tick marks (position identifying unit) of the encoder scale. The linear encoder detects the position and speed of the carriage, and controls a moving speed of the carriage and driving of the liquid discharge head. The speed of the carriage may be subjected to a servo control of a DC motor.
As a method of controlling to stop the carriage with servo control, Patent Document 1 discloses reduction of vibration and noise by smoothing speed reduction immediately after starting to reduce the speed or speed reduction immediately before stopping the carriage. Patent Document 2 discloses a control method of increasing deceleration immediately after starting to reduce speed and decreasing deceleration immediately before stopping a carriage by making the speed be gradually decreased relative to a target speed in the deceleration and thereafter be continuously decreased without using a curve requiring complicated calculation. With Patent Document 3, when a mechanical characteristic of a carriage changes with a drive range or time degradation, by changing a speed profile in response to the mechanical characteristic, stability of driving is not spoiled to thereby obtain the maximum performance.    Patent Document 1: Japanese Laid-Open Patent Application No. 2004-357374    Patent Document 2: Japanese Laid-Open Patent Application No. 2006-262571    Patent Document 3: Japanese Laid-Open Patent Application No. 2004-013810
When the servo control is continuously carried out until detection of a mechanical stop of the carriage, and the servo control is finished after the detection of the mechanical stop, it is possible to highly accurately stop a carriage within a predetermined error range from the stop position. However, there needs to be a time for stopping the carriage. At this point, if the servo control is finished in a previous stage by planning the mechanical stop of the carriage, it is possible to shorten a time before the stop although accuracy of a target stop position becomes insufficient.
It is ordinarily unnecessary to assure the accuracy of the stop position is very high in moving the carriage while printing characters. However, during an idle discharge in printing characters which is carried out by discharging inks which do not contribute to image forming while the carriage is stopped over an idle discharge receiver in every predetermined printing period, the carriage is required to be highly accurately positioned relative to an opening portion of the idle discharge receiver, for example, in an order of ±300 μm. Therefore, all controls are carried out based on this accuracy.
Therefore, it may be useful if a servo control for an operation which does not require a very high stop position accuracy ends before a mechanical stop of the carriage. If the servo control for the operation which does not require the very high stop position accuracy ends before the mechanical stop of the carriage, it is possible to avoid a delay of the start time and therefore the performance of the image forming apparatus can be maintained.